This invention relates to a dashpot with a fast idle device for carburetor throttles, particularly to a seal construction for sealing a gap defined between a vacuum chamber provided in the dashpot with the fast idle device and a rod passing through a hole made in a wall of the vacuum chamber.
The dashpot is for damping a rapid closing movement of the throttle, and the fast idle device is to cause an engine of an automobile equiped with for example a compressor for coolers to run at fast idle while the engine running is driving the compressor during stopping of the automobile. The dashpot with the fast idle device is the dashpot and the fast idle device operatively connected to each other. This kind of apparatus is shown for example in U.S. Pat. No. 3,618,582 and Japanese Publication of Pat. application No. 49-45246 (1974). They each have a vacuum chamber, a rod passing through a hole made in a wall of the vacuum chamber and axially moved with vacuum induced into the vacuum chamber, and a seal member for sealing a gap defined between the rod and the wall of the vaccum chamber. The seal member used in the Japanese Publication No. 49-45246 is a bellows type. The bellows type seal member is not proper to be used in the presence of a large pressure difference, because it shrinks due to the pressure difference to clamp the rod so that the movement of the rod will be prevented. Therefore, the bellows type seal member needs a spring to be used for spreading the seal member. In the U.S. Pat. No. 3,618,582, an o-ring is used for sealing the gap. The o-ring is not proper to be used in a dry condition, further it has defects in its precise finishing and its durability.
In the drawing of Japanese Publication of Pat. application No. 50-35971 (1975), a construction resembling the present invention is shown, wherein two vacuum chambers are divided by a partition wall through which a plunger passes, and a bellows type seal member is provided for sealing a gap between the plunger and the partition wall. Pressure difference applied to the bellows type seal member seems to be small compared with that in the Japanese Publication No. 49-45246 (1974), so that an axial movement of the plunger may be free from it.
Further, in sealing constructions, there are an oil ring and a rolling diaphragm. The former, however, has the same defects as the o-ring, and the latter has defects that its construction is complicated and has a large hysteresis.